Switch from fl_chart to syncfusion for graphs

[Gold872]

This will fix the memory leak issue with pages that have graphs on them. Syncfusion graphs don't look as pretty but are much more efficient

[Levi-Lesches]

Code looks good.

• That's a pretty significant visual downgrade, with the jagged edges... if it must be done, okay, but it would be sad
• Can you test, with the latest fl_chart version possible (use dart pub outdated or check Pub, because there was a memory leak fixed) if the issues still happen on the science page? If not, I think we can keep with the current approach, even though I don't love the API
• Besides efficiency and API, are there any other advantages to sync_fusion over fl_chart?

[Levi-Lesches]

Suggested change

	List<CartesianSeries<SensorReading, double>> getChartSeries() {
	final result = <CartesianSeries<SensorReading, double>>[];
	for (int i = 0; i < readings.length; i++) {
	result.add(
	LineSeries(
	animationDuration: 0,
	dataLabelMapper: (datum, index) => "${datum.value} $sideUnitName",
	color: colors[i],
	xValueMapper: (datum, index) => datum.time / 1000,
	yValueMapper: (datum, index) => datum.value,
	dataSource: readings[i].toList(),
	width: 2.5,
	),
	);
	}
	return result;
	}
	List<CartesianSeries<SensorReading, double>> getChartSeries() => [
	for (int i = 0; i < readings.length; i++) LineSeries(
	animationDuration: 0,
	dataLabelMapper: (datum, index) => "${datum.value} $sideUnitName",
	color: colors[i],
	xValueMapper: (datum, index) => datum.time / 1000,
	yValueMapper: (datum, index) => datum.value,
	dataSource: readings[i].toList(),
	width: 2.5,
	),
	];